A month after thousands of Southern California students walked out of about 150 schools to protest gun violence, it’s unclear how many will take part in a second demonstration set for today, the 19th anniversary of the Columbine High School shooting.

Both walkouts were planned nationwide in the wake of the Feb. 14 mass shooting at Marjory Stoneman Douglas High School in Parkland, Fla., where student activists have seized the spotlight to demand adults address gun safety.